stock tyre size is 185/65R14 on the liana as far as i know, if that is the case then the 195/60R15's you've fit are 3.2% too large and that is beyond acceptable. you need to change the tyres immediately and fit smaller ones as these will be stressing your steering and drivetrain components past what they were designed to do.
as for your fuel economy issues, the oversized tyres are contributing quite a bit since they are heavy but more so since they are too large they are causing your meter to mis-read. apart from teh tyres you shoudl consider looking into your engine setup and driving style.
engines perform best (fuel economy wise) when they are clean and perfectly setup. for this you need:
to use the correct viscosity oil,
maintian the correct spark plug gap,
ensure that the spark plugs are recieving the correct voltage,
inspect if your exhaust is not blocked by something,
check that your fuel system is under the correct pressure
ensure that your fuel filter is not blocked
check that your brakes are not binding
ensure that yout transmission is loose and fluid is full & correct
ensure that the starter disengages and there is no additional load on the engine from the ac or other "belted" systems
check your tyre pressure (once you change your tyres) to the correct size
have someone also inspect the battery to make sure it is performing up to spec.
the list can go on and on....
as for the driving of the car, i used to get a 7 average in my surf last year but now with all the stop-go traffic i'm getting 5.5!! perhaps you could help improve the average by not driving the car fast off the line, turning off the engine at the traffic lights, not allowing the car to idle for long periods etc. all these litlte things can make a HUGE difference to your fuel economy.
good luck and let us know what happens.